1. Technical Field
Embodiments described herein relate to semiconductor packaging and methods for packaging semiconductor devices. More particularly, some embodiments disclosed herein relate to shielding package-on-package (“PoP”) from electromagnetic interference.
2. Description of the Related Art
Package-on-package (“PoP”) technology has become increasingly popular as the demand for lower cost, higher performance, increased integrated circuit density, and increased package density continues in the semiconductor industry. As the push for smaller and smaller packages increases, the integration of die and package (e.g., “pre-stacking” or the integration of system on a chip (“SoC”) technology with memory technology) allows for thinner packages. Such pre-stacking has become a critical component for thin and fine pitch PoP packages. FIG. 1 depicts an embodiment of a current package on package format 100. Package 100 may include several air gaps 110 which are formed within the package during manufacture. However, air is known as a very good insulator and as such results in poor thermal conduction between the components of the package.
EMI (“electromagnetic interference”) is the unwanted effects in the electrical system due to electromagnetic radiation and electromagnetic conduction. Electromagnetic radiation and electromagnetic conduction are different in the way an EM field propagates. Conducted EMI is caused by the physical contact of the conductors as opposed to radiated EMI which is caused by induction. Electromagnetic disturbances in the EM field of a conductor will no longer be confined to the surface of the conductor and may radiate away from it. Mutual inductance between two radiated electromagnetic fields may result in EMI.
Due to EMI, the electromagnetic field around the conductor is no longer evenly distributed (e.g., resulting in skin effects, proximity effects, hysteresis losses, transients, voltage drops, electromagnetic disturbances, EMP/HEMP, eddy current losses, harmonic distortion, and reduction in the permeability of the material).
EMI can be conductive and/or radiative and its behavior is dependent on the frequency of operation and cannot be controlled at higher frequencies. For lower frequencies, EMI is caused by conduction (e.g., resulting in skin effects) and, for higher frequencies, by radiation (e.g., resulting in proximity effects).
A high frequency electromagnetic signal makes every conductor an antenna, in the sense that they can generate and absorb electromagnetic fields. In the case of a printed circuit board (“PCB”), consisting of capacitors and semiconductor devices soldered to the board, the capacitors and soldering function like antennas, generating and absorbing electromagnetic fields. The chips on these boards are so close to each other that the chances of conducted and radiated EMI are significant. Boards are designed in such a way that the case of the board is connected to the ground and the radiated EMI is typically diverted to ground. Technological advancements have drastically reduced the size of chipboards and electronics; however, this means they are also much more sensitive to EMI. Typically electromagnetic shielding is used to inhibit EMI effects. However, EMI shielding can be expensive and may have negative consequences.